Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/04/18
Area Forecast Discussion
National Weather Service Bismarck ND
335 PM CDT Mon Sep 3 2018
.SHORT TERM...(This evening through Tuesday)
Issued at 229 PM CDT Mon Sep 3 2018
Thunderstorms are the main focus in the short term period.
Overall, there are very few changes this forecast period from
the previous forecast. Convection still looks to develop between
5-6 pm cdt per latest CAM model output. This is slightly later
than earlier runs of the CAMS and also a little farther south.
However, convection does expand quickly northward into SE
Saskatchewan and SW Manitoba. Storm mode still indicates a blend
with discrete supercells possible early on (especially south)
with a transition to multicellular and QLCS later tonight. SPC day
1 outlook did expand the slight risk area a little farther east
along the Canadian border. Latest iterations of the HRRR are
supporting a possible QLCS segment pushing into the Turtle
mountains late this evening. Stronger Bulk shear along the
Canadian border with shear aligned almost due parallel to the
convective line would support this scenario.
After 06 UTC Convection appears to diminish as it moves into a
more strongly capped environment over central and eastern ND,
combined with the diurnal increase in CIN with the loss of
heating. Continued a mention of severe this early evening west and
mid to late evening central, extending as far east as a line from
around Hettinger to near Bismarck and into the Turtle mountains.
Areas east of this, at this time, would appear to have a limited
chance of severe weather late tonight.
Convection may linger through the morning over the southern James
River Valley. Although we are only expecting shower activity with
a slight chance of thunder.
Cool high pressure builds over the area through the remainder of
the day Tuesday, with temperatures in the low 60s northwest to the
lower 70s in the southern James River Valley.
.LONG TERM...(Tuesday night through Monday)
Issued at 229 PM CDT Mon Sep 3 2018
We have introduced patchy frost into the forecast across the
northwest and north central Late Tuesday night into Wednesday
morning as Cool high pressure slides into northern ND by 12 UTC
Wednesday. We utilized guidance on the cooler side of the envelope
of solutions, but not the coolest. Later shifts can adjust as
needed but we will need to monitor for possible frost/freeze
highlights mainly along and north of the highway 200 corridor.
Quiet weather is in store Wednesday through Thursday. A blend of
model guidance produces a chance of showers and thunderstorms
Thursday night into Friday morning, mainly along the International
Border in an area of warm advection and weak impulsed moving
through a quasi-zonal flow. Another wave moves through the region
Saturday into Sunday but models are not in as good agreement here,
but it does result in some slight chance pops. After the cooldown
on Wednesday, Temperatures quickly rebound to values near normal
through the remainder of the forecast period.
&&
.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 229 PM CDT Mon Sep 3 2018
VFR conditions to begin the 18Z TAF period. Scattered to broken
low vfr Ceilings this afternoon at KJMS. Otherwise clear skies
elsewhere until convection begins late afternoon/early evening.
Kept a VCTS at KISN as thinking now is convection may develop just
east of here. Added a Tempo period at KDIK and KMOT for convection
in the 03-06 UTC timeframe. With move uncertainty with convection
farther east, just added a VCTS at KBIS and KJMS using latest HRRR
for guidance on timing. After convection moves through winds
become north to northwest and remain northerly through the rest of
the 18Z TAF period. We did add a mention of MVFR ceilings
developing at KJMS late tonight and lingering into Tuesday
morning.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...TWH
LONG TERM...TWH
AVIATION...TWH
Area Forecast Discussion
National Weather Service Boise ID
908 PM MDT Mon Sep 3 2018
.DISCUSSION...Mostly clear tonight, with diminishing winds in most
areas - with the exception of Baker County, where breezy northwest
winds will persist a few more hours in the wake of the upper-level
shortwave moving across Montana. This handled well in current
forecasts, and no updates expected.
&&
.AVIATION...VFR. Mostly clear. Surface winds light and variable.
Winds aloft near 10k feet MSL west 10-20kt.
&&
.PREV DISCUSSION...
SHORT TERM...Tonight through Wednesday...Latest HRRR smoke model
brings smoke from California wildfires across our southernmost
areas tonight, spreading northeast over all but northernmost
areas by Tesday night, and continuing Wednesday. Warming trend
with Wednesday likely the warmest day of the week. Instability
and moisture will provide a slight chance of thunderstorms in
the Blue Mountains of western Baker County Wednesday afternoon.
LONG TERM...Wednesday night through Monday...Dry southwest flow
aloft will keep temperatures 5-10 degrees above normal through
Friday and slightly above normal on Saturday. This pattern will
continue to bring smoke at upper levels from fires in southwest
Oregon and northern California. Models are trending slower on the
arrival of a dry Pacific cold front, which is now expected to cross
our area on Saturday. It will be followed by breezy west to
northwest winds Saturday afternoon, and temperatures will lower to
near normal for Sunday and Monday.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...None.
&&
$$
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DISCUSSION...TB
AVIATION.....JS
PREV SHORT TERM...LC
PREV LONG TERM....JT/WH
Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
646 PM CDT Mon Sep 3 2018
.DISCUSSION...Updated for latest aviation discussion below.
&&
.AVIATION...All convection has moved well west of the three major
aerodromes and should not affect them for the remainder of the
evening and overnight hours. Tomorrow, after diminishing winds and
a few clouds overnight, surface winds will increase to moderate
levels with scattered cloudiness. Convection is expected to be too
isolated on Tuesday to warrant a mention in the current TAFs.
&&
.PREV DISCUSSION... /issued 304 PM CDT Mon Sep 3 2018/
SHORT TERM (Now through Tuesday night)...Satellite and radar
images indicate convection developing across the Mexican plateau
as well as along the seabreeze front moving westward across the
eastern portions of the CWA this afternoon. The HRRR continues to
prog convection developing across the central portions of deep
south Texas the rest of the afternoon and possibly into the
western portions early this evening. With the NAM and GFS progging
showers and thunderstorms developing with the monsoonal moisture
across northeast Mexico into southwest Texas tonight...will go
ahead and mention a chance of rain across extreme western portions
of the CWA tonight. Will also mention heavy rainfall with storms
for this evening across the same area.
Tuesday`s forecast will be challenging as the models prog some
drier air across northeast Mexico into the Rio Grande valley Tues
afternoon surrounded by monsoonal moisture to the west and
tropical moisture across the western Gulf of Mexico. Will go with
isolated showers and thunderstorms across the coastal sections of
the CWA Tues morning and spread rain chances westward Tues
afternoon with the seabreeze front. Expect showers and
thunderstorms to increase in coverage across the offshore waters
Tuesday into Tues night with the surge in tropical moisture across
the western Gulf. Temperatures should be slightly not as hot as
they have been the past couple of days but will continue to go
warmer than MOS guidance for temperatures Tues afternoon.
LONG TERM (Wednesday through Monday): Deep tropical moisture will
persist across the CWA, fueling higher rain chances through the
period. Forecast soundings show precipitable water values remaining
near or above two inches. The combination of ample moisture, daytime
heating, and weak, upper level induced troughing will support
unsettled weather and higher rain chances across the CWA. Isolated
to scattered showers and thunderstorms will continue locally through
the rest of the period as moisture lingers under modest mid level
ridging. Above normal temperatures will persist. Low temperatures
will be in the 75 to 80 degree range, while afternoon high temps
will range from the mid 90s near the coast to triple digits farther
west. The increased cloud cover and moisture will help limit heat
index values, which may periodically reach the 103 to 108 degree
range, but will generally be a skosh less than that.
MARINE:
Tonight through Tuesday night: Seas were near 3 feet with south to
southeast winds near 12 knots at buoy020 this afternoon. Moderate
to strong southeast winds will develop offshore the lower Texas
coast this evening with lower pressure across northern Mexico and
high pressure across the western Gulf of Mexico providing an
increase in the pressure gradient across the coastal waters. Will
word SCEC for the offshore waters this evening as a result. The
pressure gradient will weaken across the western Gulf of Mexico
Tuesday with Tropical Storm Gordon moving across the eastern Gulf.
Light to moderate east to southeast winds should prevail across
the coastal Tuesday as a result. Not much change is expected
across the coastal waters Tues night. A surge of tropical moisture
is expected to move across the western Gulf of Mexico ahead of
Gordon Tuesday into Tues night providing an increasing chance of
showers and thunderstorms across offshore the lower Texas coast.
Wednesday through Saturday night: Light to moderate southeast winds
and low to moderate seas will continue. The forecast position of
Gordon should be near the lower Mississippi Valley by Wednesday,
with high pressure still the main player for the lower Texas coast.
The wave models are not picking up on much potential swell in the
long term from the influence of Gordon, forecast to move across the
northeast Gulf now through Tuesday night, likely not much influence
since the residence time over sections of Gulf will not be long
enough to generate significantly bigger waves. Showers and tstorms
will remain possible in the unsettled regime of warm waters and
moist southeast flow.
&&
.BRO WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
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Please see the 00Z aviation forecast discussion below.
AVIATION...
A challenging aviation forecast is in store this period as convection
chances will largely be dominated by small scale features such as
outflow boundaries. Based on current radar data, it appears SAT will
stand the best chance for SHRA/TSRA over the next hour or so. The
next best shot at showers and storms is expected during the late
evening and early morning hours, primarily from SAT/SSF westward
into DRT. Should this scenario play out, we should see a decrease in
convection chances from late morning into early afternoon. With
daytime heating and likely plenty of outflow boundaries, another
round remains possible late Tuesday afternoon and evening.
PREV DISCUSSION... /ISSUED 245 PM CDT Mon Sep 3 2018/
SHORT TERM (Tonight through Tuesday Night)...
The coverage of showers and storms continues to increase across the
area this afternoon. The previous tropical low that was over SE Texas
yesterday is now over North Texas and is helping with the abundance
of activity in our northern CWA. For our western counties, broad
troughing continues with high moisture values streaming in from the
southwest. This same setup was in place last night and produced a
couple pockets of 4+ inches of rain fall in portions of Uvalde and
Bandera County. Cloud cover today has kept temperatures in check with
current values in the 80s and lower 90s.
For the late afternoon and evening, scattered to numerous showers
and storms are expected to continue. The initial focus of a higher
coverage area should be somewhere near the I35 corridor. Latest
satellite imagery shows that a weak boundary is moving south across
Blanco and northern Hays County. As this boundary continues to slowly
slide south it should help provide as a focus for shower and
thunderstorm activity. The latest runs of the HRRR and TTU WRF show
this area with pockets of locally heavy rainfall through the evening
hours with some weakening around the 11 pm to midnight hour. The
pockets of heavier rainfall could lead to the need for a Flood
Advisory or perhaps a Flash Flood Warning this afternoon and
evening.
The focus for possible heavy rainfall will then shift back west to
areas between Del Rio and San Antonio. Model guidance is in good
agreement that this is where the nocturnal low-level jet will set up.
Speeds at 850 mb within the jet should be around 20-25 knots with 10
knots of southerly flow on either side of the higher winds. We can
look at isentropic planes to best decipher low-level lift from the
nocturnal jets and the RAP/GFS are both showing strong upglide on the
305k surface with near saturation and lapse rates around 5 C/km in
this region. This should be more than sufficient for a decent area
of precip to develop. The HRRR shows this occurring beginning as
early as 8-9 PM with the best lift coming after midnight and
continuing through the overnight hours. Not expecting a prolonged
period of heavy rainfall, but pockets of heavier rain within the main
precip area will be possible. Will mention locally heavy rainfall in
this area too tonight.
Think we are close to needing a Flash Flood Watch for tonight,
especially for the western counties. Latest flash flood guidance is
around 1.5 inches an hour for the areas that received locally heavy
rainfall last night. PW values will be above 2 inches and these
rainfall amounts will certainly be possible. However, the heaviest
rainfall may occur southeast of this area where the current flash
flood guidance is 3+ inches in an hour. Will hold off for now but
mention the locally heavy rainfall in the grids and mention the
threat for flooding in the Hazardous Weather Outlook.
For tomorrow, the expected area of precip in our western counties
will be diminishing after sunrise with scattered activity expected
across most areas for the remainder of the day. Will show PoPs in the
30-60 percent range. Rain chances will drop off in the Tuesday Night
time frame with the favored area continuing to be in the western CWA
where the broad troughing continues.
LONG TERM (Wednesday through Monday)...
Rain chances are expected to continue to be elevated during the
long-term portion of the forecast as moisture values remain high and
the broad troughing/shear axis remains in place across the west.
There should not be much of a surface focus to help increase coverage
or amounts for much of the period. Will continue to mention locally
heavy rainfall in the HWO as any additional brief downpours on
already saturated soils could lead to localized flooding. There
could be a potential trough axis stretching into the Central and
Southern Plains by the end of next weekend. This could bring even
higher rainfall chances if it were to move as far south as the ECMWF
is showing. Will keep PoPs in the 20-30 percent range for now on Day
6/7.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 74 91 74 93 75 / 70 50 20 40 20
Austin Bergstrom Intl Airport 74 90 73 92 73 / 70 50 20 40 20
New Braunfels Muni Airport 74 90 73 92 73 / 70 50 30 40 20
Burnet Muni Airport 73 87 72 90 72 / 70 60 30 40 30
Del Rio Intl Airport 75 91 75 90 74 / 60 30 40 40 30
Georgetown Muni Airport 74 90 73 92 73 / 70 50 20 30 20
Hondo Muni Airport 74 92 74 93 73 / 80 50 40 40 30
San Marcos Muni Airport 74 91 73 92 73 / 70 50 30 40 20
La Grange - Fayette Regional 75 91 74 93 74 / 40 50 20 40 20
San Antonio Intl Airport 75 90 75 91 75 / 70 50 30 40 30
Stinson Muni Airport 76 92 76 93 75 / 70 50 30 40 30
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Tuesday morning for Dimmit-Frio-Kinney-
Maverick-Medina-Uvalde-Zavala.
&&
$$
Mesoscale/Aviation...Platt
Synoptic/Grids...17
Public Service/Data Collection...BMW
Area Forecast Discussion
National Weather Service North Platte NE
643 PM CDT Mon Sep 3 2018
.SYNOPSIS...
Issued at 312 PM CDT Mon Sep 3 2018
H5 analysis this morning had high pressure anchored
across the Mid Atlantic states with a trough of low pressure located
across the swrn CONUS. An active northern stream was noted across
southern Canada this morning with a tandem of short wave troughs.
One over southern British Columbia and a second closed system
located over southern Hudson Bay. Closer to the central and southern
plains, a nice shortwave was located over southern Colorado. This
feature has tracked north northeast this morning, and was located
over the Palmer Divide as of mid day per WV imagery. Abundant mid
level Pacific moisture, and low level Gulf of Mexico moisture,
continues to stream into western and north central Nebraska today,
and has led to abundant cloudiness across most of the forecast area
today. The exception was over northwestern portions of the forecast
area where some thin high cloudiness was noted. Readings as of 3 PM
CDT ranged from 73 at O`Neill to 82 at Valentine.
&&
.SHORT TERM...(This evening through Tuesday)
Issued at 312 PM CDT Mon Sep 3 2018
Tonight and Tuesday: Fog potential and precipitation
chances are the main short term forecast challenges. With respect to
precipitation chances tonight: A robust upper level disturbance
continues to lift across eastern Colorado this afternoon. The latest
NAMNest and HRRR solns lift this activity into southwestern
Nebraska, dissipating it over the central and eastern Sandhills this
evening. Fairly weak deep layer shear and meager CAPE will be
present across swrn Nebraska through mid evening, so not expecting
much of a severe threat attm. Some adjustments were made pops
especially this evening as the models have a hard time, lifting this
activity into the western sandhills and nwrn Nebraska. That being
said, adjusted pops downward, in the north central and west
overnight as the focus for thunderstorms shifts into central and
eastern Nebraska overnight. West of the main area of convection,
light easterly and southeasterly winds are expected overnight. With
continued favorable low level moisture advection, will insert a
mention of fog in the forecast for the bulk of the CWA overnight.
Will keep the mention patchy as any isolated thunderstorms
overnight, would not be favorable for fog formation. Overnight lows
will continue to be mild with the expected cloud cover. Readings
will range from the upper 50s in the panhandle to the upper 60s in
the east. On Tuesday, fog will linger into the mid morning hours
before burning off. However, skies will remain cloudy to mostly
cloudy across the forecast area as abundant mid and low level
moisture continues to be pushed into the forecast area from the
south. This will limit highs to the 70s tomorrow. Late Tuesday
afternoon, a decent shortwave will lift from NE Colorado into SW
Nebraska. Showers and storms will develop over NE colorado and lift
into the forecast area through Tuesday evening. Confidence is fairly
high for pcpn Tuesday evening as there is good model agreement
between the NAM12, GFS, WARW and HREF ensembles.
.LONG TERM...(Tuesday night through Monday)
Issued at 312 PM CDT Mon Sep 3 2018
The threat for precipitation will carry over into Tuesday night
before tapering off Wednesday morning. Surface high pressure will
drop south across the Dakotas into Minnesota. This feature will
force a cool front through the forecast area and focus
precipitation to the south of the area over Kansas. This will
bring a temporary reprieve to precipitation Wednesday into
Wednesday night. The high will migrate into the northern Great
Lakes Thursday into Friday. Southerly flow will commence across
the area, leading to an increased chance for showers and
thunderstorms across the central and eastern forecast area later
in the week. A shortwave trough, followed by ridging building into
the western CONUS will facilitate drier and warmer conditions for
the weekend into early next week. Readings will rebound back into
the lower to middle 80s with lows in the 50s and mainly dry
conditions are expected.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 630 PM CDT Mon Sep 3 2018
Latest radar display shows showers and thunderstorms moving
northeastward across southwest NEB south of Interstate 80.
Meanwhile, latest surface obs show MVFR ceilings across much of
southwest and south central NEB. Current thinking is isolated to
scattered showers and thunderstorm will be a threat mainly to
southwest NE south of the Sandhills through the evening hours.
Thereafter spotty showers and thunderstorms will be possible
across the eastern portions of the local forecast area with
activity expected to be mainly outside of the area to the east.
Increased chances for showers and thunderstorms then return to
the area tomorrow afternoon with mention of TS at both KVTN and
KLBF terminals currently. Otherwise, threat for patchy fog for
much of the area late tonight into tomorrow morning. MVFR ceilings
expected to affect much of southwest NEB, Sandhills and north
central NEB tonight into morning.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Buttler
SHORT TERM...Buttler
LONG TERM...Buttler
AVIATION...ET
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
931 PM CDT Mon Sep 3 2018
.UPDATE...
931 PM CDT
Evening Update...
Convective activity has trended substantially downward from
earlier this evening. RAP mesoanalysis data depicts 1000 J/kg of
MUCAPE lingers across the southern 2/3 of the forecast area at
this hour, though convective outflow and diurnally induced cooling
have stabilized the boundary layer with respect to surface
convection. Combined outflows from earlier extensive convection
have pushed the effective frontal boundary to the ILX/LOT cwa
border region, though 20-25 kt southerly flow in the 925-850 mb
layer exists above the stable low levels, which could continue to
support some isolated shower or thunderstorm development late this
evening. Some high-res guidance depict some weak/isolated shower
development across parts of the region through about midnight, and
have maintained some slight or low-chance category pops for this.
Overall however, larger scale forcing appears to be on the
decrease with short wave lifting northeast across the Upper
Mississippi Valley overnight, and weak height rises depicted
around the west/northwest periphery of the upper level ridge
across the mid-Atlantic and Ohio Valley regions. Threat of
widespread heavy rainfall appears low, though with such saturated
ground from recent rounds of excessive rainfall, and the potential
for additional isolated precip over the next few hours, will hang
onto the flash flood watch through its midnight expiration across
far northern IL.
Otherwise, may see some patchy fog development overnight tonight,
with extensive wet ground across the northern half of the cwa and
small temp-dew point depressions. Southeast winds, while light at
less than 10 mph, may keep fog from becoming too thick or
extensive however. Something to monitor overnight.
Ratzer
&&
.SHORT TERM...
340 PM CDT
Through Tonight...
Thunderstorms continue to develop across much of northern
Illinois and northwest Indiana this afternoon. Despite several
hours of development today, the atmosphere remains highly
unstable, supported by high dewpoint air and steep low level lapse
rates. Shortwave energy still moving overhead at this time, with
additional focus now along southward moving front in place across
northern Illinois. So do think there will be additional
development over the next several hours, and although may persist
into the mid evening time frame, should see substantial
diminishing coverage and intensity during that time. Despite a
lowering trend of overall shear, there remains enough for some
isolated organized development this afternoon. This will provide
an additional threat of a few stronger storms capable of producing
damaging winds. An additional continued threat will be heavy
rainfall and flooding, as every storm will likely produce
torrential rainfall.
Rodriguez
&&
.LONG TERM...
340 PM CDT
Tuesday through Sunday...
Overview...The active pattern continues through the extended with
multiple chances for showers and storms. Hot and humid conditions
also continue through Wednesday, but a cold front brings cooler
temps to the region for the latter half of the week.
Isolated afternoon storms are possible Tuesday, but I have low
confidence in coverage and timing. I have higher confidence in hot
and humid conditions resulting in heat indices in the mid to upper
90s. Afternoon storms should dissipate as the sun goes down.
The next chance of precip arrives ahead of a cold front Wednesday
morning. I have high confidence in rain across the area. Given the
slow nature of the front, I think heat indices will once again be in
the 90s.
Luckily a cooler air mass follows the cold front with highs only in
the 70s to around 80 Thursday. Guidance continues to indicate
showers and some storms are possible mainly along and south of I-80
Thursday into Friday morning thanks to an upper level wave over
northern IL. I have medium coverage in precip and thunder
occurrence.
Precip chances increase across the forecast area Saturday as an
upper level wave and surface low move over the region. I have much
higher confidence in precip Saturday than Sunday. Sunday may be dry,
but I left low chance precip chances as some models have the low
traveling a bit slower. Zonal flow aloft would suggest the active
yet cooler pattern continues as waves pass over the region early
next week.
JEE/Rodriguez
&&
.AVIATION...
For the 00Z TAFs...
654 pm...Forecast concerns are thunderstorms early this
evening...chance of fog Tuesday morning and a chance of
thunderstorms Tuesday afternoon.
The back edge of the thunderstorms is currently between mdw/gyy
and should be weakening and slowly shifting east/northeast of the
next few hours. Isolated convection may continue south of the
terminals through the evening but other than a few showers...the
rest of tonight currently looks quiet for the terminals. Chances
for thunderstorms Tuesday afternoon look low. There may be a lake
breeze that forms near the lake that could aid afternoon precip
development. Tuesday will be very warm and humid with quite a bit
of instability but not much of a focus for development. Opted to
add prob mention with this forecast but confidence is low.
Generally easterly winds early this evening are expected to turn
more southeasterly later this evening and southerly overnight.
Wind directions will become south/southwest by mid morning with
speeds increasing into the 10-15kt range. Some gusts are possible
by afternoon. Winds may turn more southerly or south/southeasterly
by late afternoon/early evening.
Patchy fog is possible overnight into Tuesday morning but
confidence is low. Added 6sm mention at dpa/gyy but trends will
need to be monitored later this evening/overnight. cms
&&
.MARINE...
340 PM CDT
A period of south winds of 15-25 kt begins Tuesday. Winds sharply
turn north 10-20 kt, psbly to 25 kt behind a cold front
Wednesday. A small craft advisory may be needed for hazardous
waves Wednesday night into Thursday morning. Northeast winds
diminish as a high builds over the western lakes Thursday.
Northeast to east winds are expected through at least the first
half of the weekend.
JEE/Rodriguez
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flash Flood Watch...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
ILZ011-ILZ012 until midnight Tuesday.
IN...None.
LM...None.
&&
$$
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Area Forecast Discussion
National Weather Service San Francisco Bay Area
843 PM PDT Mon Sep 3 2018
.SYNOPSIS...Look for seasonably warm conditions inland while cooler
temperatures prevail at the coast in response to the marine layer.
Inland areas cool by a few degrees on Wednesday when a weak trough
pushes inland to our north. Inland temperatures warm back to above
average across the interior late in the week as high pressure builds
over the region.
&&
.DISCUSSION...as of 8:43 PM PDT Monday...Onshore breezes will
carry coastal stratus and patchy fog back inland tonight and
Tuesday morning. Hazy and smoky conditions are still prevalent
mainly aloft; the Sep 3 18z run of the HRRR modeled near surface
smoke indicates hazy and smoky conditions over the Bay Area going
through late Tuesday evening.
A long wave trough remains located over western Canada and near the
Pacific Northwest. 500 mb mean height forecasts lean toward a medium
long wave ridge developing over California by early to mid next
week.
The upstream air flow over the Pacific Basin is chaotic and highly
amplified. Recent medium range forecasts have been leaning toward
a large scale block developing over the North Pacific, aside from
ok agreement that the pattern will be nearly stationary they have
otherwise not been settling on any particular solution or
atmospheric block type, season-wise it is a bit early for blocks;
the Sep 3 12z ECMWF shows short lived sharply split north-south
250 mb jet stream flow advancing eastward of Japan Mon through Wed
next week. Part of the models struggle could be due to handling
remnant deep tropical moisture well NW of Hawaii between 174 and
175 degrees west longitude becoming ingested into a low center
W-SW of the Aleutians (and east of this low is a ridge with warm
air advection fueling or building ridge heights) eventually the
low incorporates more moisture from presently tropical cyclone
"Jebi" according to the GFS.
Growing differences in the medium range model output itself is a
sign the large scale pattern is undergoing change, thus with the
aforementioned description it is a primarily low confidence forecast
for downstream over us late in the medium range. Climatology is
the most reliable indicator out near the end of and beyond the
medium range or extended period. Best guess at this point for this
week and next is that we`ll continue to have more of the usual
September weather late night and morning inland intrusions of coastal
stratus and fog and onshore breezes strongest each afternoon and
evening, ridge strength /subsidence/ determining the depth of the
marine layer. Dry through the extended forecast period.
&&
.PREV DISCUSSION...as of 1:54 PM PDT Monday...Clouds have mostly
mixed out over inland areas except for the typical spots along the
coast and around portions of the Monterey Bay. This has allowed
for modest warming in the interior where temperatures are being
reported in the 80s with 60s and 70s more common near the coast
and around the bays. However, with the marine layer between
1,800-2,000 feet in depth, do expect daytime highs to be slightly
cooler compared to yesterday for inland areas. With the deep
marine layer, look for low clouds to push back inland overnight
and spread into most valley locations. This will hold overnight
lows in the 50s for most urban areas once again.
Not much change expected on Tuesday with temperatures near to
slightly above seasonal averages across the interior. Near the
coast, low clouds will linger later into the morning with cooler
onshore flow. A weak short-wave trough is then forecast to push
inland to our north which will help weaken the ridge aloft on
Wednesday. This may also help to deepen the marine layer Tuesday
night which will result in a slight cooling trend Wednesday
afternoon. However, if the disturbance helps to mix out the marine
layer, coastal areas may actually see more sunshine on Wednesday
compared to previous days.
High pressure over the Pacific will then build into southern and
central California late in the week. This will result in
temperatures rebounding back to above seasonal averages, especially
inland while the marine layer will likely keep cooler conditions
near the coast. Dry weather conditions are also likely to prevail
through the forecast period.
&&
.AVIATION...as of 4:45 PM PDT Monday...Lots of stratus along the
coast. Marine layer is slightly lower today but latest models
show little change in 500 mb heights through 24 hours. If this
verifies stratus conditions would be similar to yesterday. But if
the marine layer compresses more than expected tonight there
would be less clouds in the SFO Bay Area. Will have to monitor for
that.
Vicinity of KSFO...VFR through the airport evening rush. MVFR
cigs after 12Z. West to northwest winds 18-20 kt through 04Z.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Stratus rolling across MRY Bay this
afternoon but clouds remain north and west of MRY and SNS.
As usual the clouds will move over MRY and SNS a 02Z.
MVFR/IFR ceilings will transition to VFR within the next hour
or two, though areas of low clouds will likely hang around parts
of the Monterey Peninsula through much of the day. More low clouds
with likely IFR ceilings in the evening/overnight hours.
&&
.MARINE...as of 04:41 PM PDT Monday...Locally moderate and gusty
winds will continue into the evening hours near the Golden Gate
and Angel Island, as well as the outer waters north of Point
Reyes. For other locations, winds are generally forecast to be
less than 20 kt through the middle of the week. A light to
moderate northwest swell will persist through the week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm
SCA...SF Bay until 9 PM
&&
$$
PUBLIC FORECAST: Canepa/RGass
AVIATION: W Pi
MARINE: Rowe
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Area Forecast Discussion
National Weather Service Pittsburgh PA
757 PM EDT Mon Sep 3 2018
.SYNOPSIS...
Heat, humidity and isolated afternoon thunderstorms are
expected through mid-week. A late week cold front will bring
better rain chance and more seasonable temperatures.
Temperatures will be ten degrees cooler next weekend.
&&
.NEAR TERM /THROUGH TUESDAY/...
Evening Discussion: No major changes have been made to the
forecast.
Previous Forecast: Scattered showers and storms have continued
to developed on the lake breeze downwind of Lake Erie and
outflow boundaries. This will transition through the forecast
area through the evening hours across the northwestern 1/3rd of
the forecast area. Farther southwest in eastern Ohio, northern
West Virginia, and southwestern Pennsylvania, enough subsidence
should offset scattered storm development. HRRR wants to place
isolated storms in this region, but several other of the CAMS do
not. Elected to keep an optimistic dry forecast rolling, even
though most would like the rainfall for their lawn. Can`t rule
out a pop up storm, but if any develop they will be brief and
not last long given them will quickly rain themselves out.
Valley fog will develop overnight, most likely in the Allegheny
river region given they will experience measurable rainfall
during the day. Also the deeper gorges of West Virginia.
Overnight lows will remain humid as dewpoints reside in the
upper 60s to lower 70s.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
Heat remains the main story for the short term with Wednesday
being the hottest day of the week. Heat index values will push
into the upper 90s outside of the mountains, but dewpoints will
be in the 69-71F range which will be two degrees short of us
reaching heat advisory criteria /100-100F threshold needed/.
As the mid atlantic ridge weakens mid level heights fall
allowing a weak baroclinic zone to drop south. As it moves
through the forecast area during the afternoon Thursday ramped
up pops to likely as their will be plenty of moisture to tap
even through the trigger mechanism is fairly weak. It is
possible the boundary could cross northern areas precip free
since it will be moving through during the early morning hours.
As this point, do not see a high water nor severe threat. Wind
flow is not that strong. There should be enough movement in the
storms despite PWATS around 1.7 inches that negate a flash flood
threat. If I had to pick which is a greater concern at this
juncture it would be flash flooding.
The only location that could set a record high Tuesday and
Wednesday would be Dubois as benchmarks reside at 88. All of the
longer period of record sites, daily maximums sit in the low
100s.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Highlights:
- Heat Wave is over
- Return to Active Pattern
- Temperatures just above near normal
Overall good agreement amongst long range ensembles for the
extended. By this weekend, there are differences where the cold
front stalls/ washes out over northern West Virginia which will
have affects on pop grids. The next weather system crosses
Sunday. This will bring showers and storms over much of the
region as the low tracks across Lake Erie. GFS is much faster
getting the system through by as much as 12 hours over the
ECMWF.
The good news is the H5 anti-cyclone weakens allowing the
westerlies to setup across the area. This spells a little relief
from the hot weather as daytime highs settle back into the upper
70s to lower 80s save for the mountains. The mean off the
statistical guidance is just below the high end of the
temperature spread, so mid 80s are possible Friday, before a
cool down this weekend.
&&
.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
VFR conditions and light wind will be the general rule, as a
strong ridge of high pressure remains in control. However, a
thunderstorm may roll through FKL through 02Z. Also, patchy
valley fog is possible late tonight, especially at FKL/DUJ,
where rain has fallen today. Most fog will dissipate by 13Z,
followed by scattered cumulus and another possible round of
isolated to scattered convection.
Outlook...
The next chance for general restrictions will come Thursday with
an encroaching frontal boundary.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...None.
OH...None.
PA...None.
WV...None.
&&
$$
Area Forecast Discussion
National Weather Service Great Falls MT
515 PM MDT Mon Sep 3 2018
.UPDATE...
Quick update to reflect a quicker frontal passage than indicated
in our grids, primarily using the HRRR model.
&&
.SYNOPSIS...
A cold front will advance through the region tonight, causing
increasing clouds but otherwise remaining dry, except for an
isolated mountain rain shower. Temperatures on Tuesday will reach
the 60s and 70s, under mostly clear skies. Mainly dry, and warmer
conditions are expected through the end of the work week.
&&
.AVIATION...
Updated 2315Z.
A strong dry cold front continues to move south through the
region and will reach KLWT just after 00z this evening. A brief
period of 1 to 3 hours of gusty winds will occur behind this
frontal passage, before loss of daytime heating/mixing begins to
stabilize the lower atmosphere and winds begin to gradually
subside. CIGS will develop and lower behind this front,
especially over north-central MT, but will likely remain within
the VFR range. A few mountain-obscuring showers are possible
along the Rocky Mountain Front and the isolated mountain ranges to
the east through 12Z/Tue. A surface high pressure quickly builds
across the region overnight, resulting in light northeast to east
winds continuing into Tuesday.
&&
.PREV DISCUSSION...
/ISSUED 301 PM MDT Mon Sep 3 2018/
Tonight through Wednesday...A cold front has moved across the
HiLine counties west of Havre. Pressure rises behind the front are
producing northwest winds around 20 kts, with gusts to around 35
kts. Expect the front to continue advancing south and east through
the evening. Clouds are increasing as well, but are not expected
to produce any more than an isolated mountain shower. Winds
gradually decline overnight as the surface low moves away to the
east, and high pressure builds over the region. Temperatures trend
about 10 degrees colder on Tuesday amid this cooler airmass, with
smaller changes for Southwest Montana. The westerly flow aloft
transitions to weak ridging on Wednesday. This will yield
continued fair weather with light winds and warmer temperatures.
Wednesday night through Monday...Weak ridging moves east across
the region through the end of the week. A generally west to
southwest and more moist flow sets up behind the ridge bringing
an isolated chance for afternoon showers through the end of the
week. GFS continues to show much more shower development
potential whereas the ECM keeps things mostly dry. Based on the
trend this week, have leaned towards the drier solution. Another
frontal system moves into the Pacific Northwest Friday, beginning
to influence Montana Friday night. With good jet support expect
winds to pick up out of the west Friday and Saturday, with
strongest winds along the Northern Rocky Mountain Front. This
system does not appear to be overly potent and breaks up over the
mountains as it moves east through southern Canada. There will be
a chance for isolated showers along the northern Rockies and
along the Canadian border Saturday and Sunday as a result.
Temperatures slowly warm to the mid 80s by Friday as a result of
warm air advection in southwest flow, dropping into the low 70s
to mid 60s for the weekend. Models remain in solid agreement with
a continued progressive pattern until at least the start of next
week. Differences emerge Tuesday into Wednesday but both GFS and
ECM look to favor a slight building of high pressure over the
desert southwest by the middle of the week.
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 43 64 42 77 / 0 0 0 0
CTB 38 61 38 73 / 0 0 0 0
HLN 47 69 44 81 / 0 0 0 0
BZN 43 70 43 80 / 0 0 0 0
WEY 33 72 34 75 / 0 0 0 0
DLN 42 72 41 80 / 0 0 0 0
HVR 42 64 42 77 / 0 0 0 0
LWT 41 62 40 75 / 10 0 0 0
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
http://www.weather.gov/greatfalls
Area Forecast Discussion
National Weather Service Tucson AZ
330 PM MST Mon Sep 3 2018
.SYNOPSIS...Scattered thunderstorms mainly from Tucson
southward and eastward today. A gradual drying trend should prevail
after Tuesday, with isolated thunderstorms mainly east of Tucson.
Daytime temperatures will be a few degrees below average through
Wednesday, then warming to near or slightly above average Thursday
into this weekend.
&&
.DISCUSSION...Satellite imagery showed mostly sunny to partly cloudy
skies across much of southeast Arizona this afternoon. A few showers
and thunderstorms were ongoing mainly south of Tucson to the Int`l
border and across the White Mountains northeast of Safford. These
storms were fairly well-behaved at the moment, and were moving
toward the east at around 15 kts. Of note, the HRRR solutions have
been panning out well so far this afternoon with the timing,
location and movement of convection. If this trend continues, we`ll
see isolated to scattered storms continuing into the early evening
and we should be back in clear air mode by midnight.
The upper trough which has been driving our weather will continue to
do so much of this week. Showers and thunderstorms will occur again
on Tuesday, though coverage and intensity should be slightly less
than today. Continued westerly flow will work to push deeper
moisture eastward by Wednesday, confining convection to areas mainly
east and south of Tucson, and especially near the AZ/NM border. The
trough finally moves out on Friday with high pressure off the
southwest coast of California elongating and pushing its way into
the region. This will dry things out even more on northerly flow
aloft. A bit of low level moisture may still spark storms near
terrain this weekend, but we`ll keep PoPs limited to the slight
chance category.
High temperatures through Wednesday will be 3-5 degrees below
average. An increase in heights and thicknesses will then warm
temperatures to near or even slightly above average Thursday into
this weekend.
&&
.AVIATION...Valid through 05/00Z.
Scattered -TSRA/-SHRA through this evening, and isolated -TSRA/-SHRA
Tuesday afternoon. Cloud decks from KTUS east, apart from lower
thunderstorm bases, generally 8k-12k ft AGL. West of KTUS mainly FEW-
SCT clouds around 10k ft AGL. SFC wind variable in direction and
less that 12 kts, except brief gusts to 40 kts near stronger TSRA.
Aviation discussion not updated for TAF amendments.
&&
.FIRE WEATHER...Scattered thunderstorms into this evening with
isolated showers and thunderstorms on Tuesday. A drying trend will
then occur Tuesday night into the upcoming weekend, with isolated
mainly afternoon and evening thunderstorms generally across Fire
weather zones 152 and 153. Expect terrain driven 20-ft winds at less
than 15 mph, with brief strong gusts near thunderstorms.
&&
.TWC WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
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